Bio-Rad Quantity One 1-D Analysis Software - Manual (Page 185)

Quantity One User Guide
7-10
Global Background Subtraction
Note: If you select Global Background Subtraction in the Volume Report Options
dialog, but do not define a background volume as outlined below, you will
effectively select no background subtraction.
Global background subtraction calculates a single background intensity for the entire
gel. This average background intensity is then subtracted from all the volumes in the
gel. The steps for calculating global background subtraction are:
1. Create a volume using one of the volume tools in a representative background
region of the image (i.e., a region where there is no data and where the average
pixel intensity appears to be the same as the background intensity surrounding
your data).
2. Double-click on the volume to open the Volume Properties dialog, and select the
Background option button.
Fig. 7-8. Defining a background volume object.
The average intensity of the pixels in the background volume will be calculated and
subtracted from each pixel in all standard and unknown volumes. Any pixels inside
the volumes that have the same intensity as the average background will be reduced to
zero, thereby eliminating them from the quantitation.